Globally, the demand for petroleum feedstock has constantly increased in the past few years and consequently the quality of available crude oils has decreased significantly. The decreasing quality has thereby resulted in a requirement for upgrading the low quality crude oils. Particularly, the highly acidic crude oil has to be processed to provide for the increasing demand for hydrocarbon resources, which also enhances the refiner's profitability due to lower price in comparison with low acidic crude oils. Currently, there are several refining process for processing the low quality crude oil.
However, there are many serious problems raising during storage, refining, and transportation of highly acidic crude oils due to its strong tendency for corrosion. More specifically, corrosion of metal surfaces, which ultimately requires frequent changes of the corroded parts or use of expensive refractory metals. The corroded metallic compounds cause serious plugging problems in piping.
The low quality crude oil containing large amount of organic acid has low economic value due to difficulties in processing the same. Most of the organic acids have carboxylic acid functional groups. More specifically, Naphthenic acid, a representative organic acid compound having carboxylic acid functional group on hydrocarbon molecules of long chain paraffin with cyclopentane is further more difficult to process.
A number of methods have been suggested to de-acidify acidic petroleum oil. The methods comprise of adding basic compounds to neutralize acidity of petroleum oils. Methods of adding Polymeric compounds having enough basicity to trap or neutralize acidic compounds in crude oil were also disclosed in the past to decrease acidity of crude oils. Further, naphthenic acid compounds, which are representative acidic compounds found in crude oil, can also be converted to esteric compounds through reaction with alcoholic compounds in the presence or absence of catalyst. Furthermore, extractive separation is also known for separating organic acidic compounds, including naphthenic acid compounds, from petroleum oil. In addition, various solvents were tried to separate organic acidic compounds, such as salt and water-oil emulsion containing concentrated naphthenic acid compounds. Also, catalytic processes have been evaluated, typically with mild reaction conditions. The known processes tend to treat merely a cut of the crude stream and not the whole crude stream. Therefore, in order to protect metal surface from corrosion, corrosion inhibitors can be used to passivate metal surface prior to being subject to acidic crude oil.
U.S. Pat. No. 6,325,921 B1 (Andersen) discloses a method of removing metal impurities contained in heavy petroleum feedstock by processing a particular cut of the crude oil with supercritical water in the presence of a solid catalyst. Andersen teaches fractionation to produce an atmospheric residue which is then treated with zirconium oxide catalyst. The fractionation is typically performed within a refinery and not at the site of production. Thus, Andersen describes transporting corrosive acidic crude to the refinery site. Furthermore, Andersen teaches the exposure of the fractionation column to acidic crude, thus resulting in a costly refining process. Finally, the Andersen method suffers from the production of sludge and coke formation that quickly plug lines.
U.S. Pat. No. 4,840,725 (Paspek et al) discloses a process for conversion of high boiling hydrocarbon to low boiling petroleum with water of supercritical condition in the absence of catalyst. Paspek does not teach the removal of acidic compounds nor would the process as taught by Paspek remove such compounds. Furthermore, Paspek does not teach treating the crude at the on-site production facility, so the crude identified in Paspek must be transported, which would further lead to corrosion when the crude is acidic. Finally, the method described in Paspek leads to the formation of coke, however the amount of coke produced is less than the conventional methods.
U.S. Pat. No. 4,818,370 (Gregoli et al) discloses a process for converting heavy hydrocarbon, such as tars and bitumen to light hydrocarbon by supercritical water in the presence of brine.
There are number of problems associated with simply de-acidifying acidic crude oils. However, methods to de-acidify highly acidic crude oils disclosed in the prior art require either special chemicals which are not present in the original crude oil or require employment of complicated processes which cannot be conducted at an on-site production facility. Additionally, the methods disclosed in the prior art either degrade the quality of the crude oil or otherwise do not significantly improve or upgrade other qualities of crude oil, such as viscosity, density, and sulfur, and metals content.
The prior-arts also propose the use of corrosion inhibitors to passivate metal surface in order to protect metal surface from corrosion, corrosion inhibitors. More specifically, organic polysulfide or phosphites or phosphoric acid were proposed to provide good performance to form protective film on metal surface. However, this technique suffers from the additional expense of the injection and re-injection of inhibitors in order to maintain sufficient thickness of the protective film. Also, each metal item contacting the acidic crude must be contacted with an operable amount of the corrosion inhibitor to be treated, instead of merely removing the problematic functional group from the crude.
Therefore, an efficient process is needed to process acidic crude oil at the refinery with minimum requirement of metallurgy changes and corrosion inhibitor usage. It would be further advantageous to propose a process which can cause conversion of crude oil to valuable products while reducing the acidity.
Further, acidity of crude oil is measured through titration with potassium hydroxide to estimate total acid number (“TAN”) as milligram of KOH required to titrate one gram of crude oil. Crude oils having a TAN over 0.5 are generally regarded as acidic crude oils. This definition can change between countries or a lower TAN can be specified for an end product. It is also observed that the naphthenic acid compounds contributing to TAN normally concentrate in the heavier fraction of the crude oil boiling above 200-230° C. The present invention addresses acid in crude and is therefore useful for reducing acid and offers a way to process high acidic crude oils in petroleum refineries with minimum changes in the metallurgy of equipments and use of corrosion inhibitors.